1. Field of the Invention
The present invention relates to an improvement in an illumination light source system, a projector having the illumination light source system, and a method of controlling a projector.
2. Description of the Related Art
An illumination light source system using a high brightness discharge lamp (for example, extra-high pressure mercury lamp) as a light source is known as an illumination light source system for a projector which projects image information of a personal computer (hereinafter, referred to as PC), or the like in a meeting, for example.
The discharge lamp requires a predetermined time to achieve stable emission after the start of lighting although high brightness can be achieved at low costs.
Consequently, solid-state light-emitting elements such as red (R), green (G), blue (B) light-emitting diodes or organic EL elements are practically used as a substitute light source for a discharge lamp.
The use of the solid-state light-emitting elements as an illumination light source of a projector enables high-speed startup of a projector and an environmentally friendly projector.
A technique which obtains a color projection image by using a blue laser diode as a first light source (excitation light source) is known as an illumination light source using solid-state light-emitting elements (refer to Patent Document 1: JP 2011-13316A and Patent Document 2: JP 2010-85745A). With this technique, laser light as excitation light emitted from the blue laser diode irradiates a phosphor, RGB color light is generated by the excitation of the phosphor, and a color projection image is obtained by controlling the tones of RGB color light on a pixel-to-pixel basis by using a light modulation element such as DMD (Digital Micromirror Device).
The illumination light source system described in Patent Document 1 comprises a light-emitting plate (fluorescent wheel) including a phosphor layer having a plurality of segment areas divided in the rotation direction and generating fluorescent light upon the reception of excitation light, and a transmission area which transmits the excitation light; a first light source which irradiates a phosphor with the excitation light; a second light source which emits light of a wavelength different from that of the fluorescent light emitted from the phosphor and that of the excitation light; a condensing optical system which condenses the light emitted from the light-emitting plate (fluorescent wheel) and the light emitted from the second light source on the same light path; and a light-emitting controller which controls the emission of the first and second light sources.
In order to prevent color mixing in a boundary of adjacent segment areas, the light-emitting controller turns off the first light source so as not to emit light, and turns on the second light source so as to emit light.
The illumination light source system described in Patent Document 2 includes a rotation plate (fluorescent wheel) in which phosphors are arranged at intervals in the circumference direction, an excitation light source which irradiates the phosphors with excitation light, and a light-emitting controller which controls the excitation light source to be turned off when an area between the phosphors is located on the optical axis of the excitation light source.
The invention described in Patent Document 1 prevents color mixing in a boundary because the first light source is turned off in a boundary of adjacent segment areas. However, the phosphors of the fluorescent wheel are directly irradiated with the excitation light, so that an irradiation time to the segment areas per unit time (1 second) is constant regardless of the rotation speed of the fluorescent wheel per unit time (1 second). For this reason, the fluorescent property of the phosphors may be deteriorated if the microscopic areas of the segment areas are continuously irradiated with the excitation light.
Consequently, an illumination light source in which a reflection/transmission member having a transmission area and a reflection area is provided in an emission light path of a first light source which emits excitation light and a fluorescent wheel is provided in at least one of a transmission light path formed by the transmission area and a reflection light path formed by the reflection area is developed. In this illumination light source, the emission light path of the excitation light is switched between the transmission light path and the reflection light path in a unit time, so that an irradiation time to the phosphor per unit time can be changed by switching the transmission light path and the reflection light path during the rotation of the fluorescent wheel per unit time (1 second), so as to prevent a deterioration in a fluorescent property of a phosphor.
However, even with the illumination light source in which the reflection/transmission member is provided in the emission light path of the first light source which emits the excitation light, color mixing occurs due to the irradiation of the excitation light when excitation light passes through the boundary area between the reflection area and the transmission area.
In order to prevent such occurrence of the color mixing, it is considered to turn off the excitation light source when the boundary area between the reflection area and the transmission area crosses the emission light path of the excitation light source. However, a brightness of an image is lowered when the excitation light source is turned off.